Field
The disclosed and claimed concept relates generally to small power sources that are electrically connectable with a power grid and, more particularly, to a controller and a method for controlling the provision of power from a small power source to the power grid.
Related Art
Numerous types of power sources are known in the relevant art. Power sources can include power plants that are operated by utilities for large scale power generation and can also include smaller power sources that are energized by renewable power sources such as photovoltaic (PV) power sources, windmill power sources, and the like. Such smaller power sources typically have nowhere near the generation capability of, for instance, a fossil fuel powered generator employed by the electric utilities, but such small power sources are nevertheless meaningful on some level. The expression “small power source” and variations thereof herein is intended to refer to power sources that are not conventional electrical utilities and that are not otherwise under the control of a conventional electrical utility or other concern that controls a given power grid.
By way of example, a homeowner might own a home that includes a local electrical network that is electrically connected with a power grid, with the power grid being electrically connected with an electrical generator that is controlled by an electrical utility. The local electrical network typically will include a load center or circuit breaker panel, by way of example, that is electrically connected with the power grid and that further includes various electrical loads that are electrically connected with the load center. Such electrical loads typically include domestic lighting systems, HVAC systems, hot water heaters, and electrical plugs for the connection and operation of refrigerators, television sets, clothes dryers, and the like without limitation. If the local electrical network additionally includes a small power source, such as a photovoltaic (PV) power source by way of example, the PV power source would be connected with the load center and would provide electrical power to the load center and thus to the local electrical network when the PV array has ambient light impinging thereon in a known fashion.
Since the load center is electrically connected with both the power grid and the small power source, some or all of the power that is generated by the small power source is delivered to the load center and is consumed by the loads that are connected therewith, thereby reducing the amount of power that would be otherwise be obtained from the power grid and consumed by the local electrical network. If the small power source generates more power than is consumed or otherwise used by the loads of the local electrical network, the excess power can be transmitted into the power grid, and the homeowner will be granted an electrical credit for the power provided to the power grid. While such systems have been generally effective for their intended purposes, they have not been without limitation.
As is generally understood, a power grid desirably has a fairly stable voltage that does not undergo rapid changes. While a power grid will almost certainly experience changes in its voltage, such voltage changes occur only gradually as a function of time. While most power grids have not typically experienced significant voltage fluctuations when loads are connected therewith, some power grids have experienced undesirable voltage fluctuations when certain small power sources that are connected with the power grid periodically supply power to the power grid.
By way of example, if in a given geographic area a large number of homeowners each have PV power sources connected with their local electrical networks, a semi-cloudy day can result in rapid changes in the power that is being supplied to the power grid by the PV power sources. This is because any given cloud can simultaneously affect a large number of PV power sources. Such a cloud can cause a large number of PV power sources to produce relatively little electrical power when the cloud is between the sun and the PV power sources. However, a gust of wind can move the cloud away from the PV power sources, at which time the PV power sources might all approximately simultaneously suddenly begin to provide surplus power to the power grid.
In order for such surplus power to flow from the local electrical networks to the power grid, the voltages of the local electrical networks must be greater than that of the power grid voltage. The sudden addition of electrical power to the power grid from a large number of PV power sources at a higher voltage than that of the power grid can sometimes result in the voltage of the power grid itself correspondingly increasing, depending upon many factors including the overall health of the power grid. Likewise, if a large number of PV power sources are providing surplus power to the power grid and a large cloud suddenly reduces the amount of PV power that is being supplied to the power grid, the power grid can experience a drop in power grid voltage depending upon a number of factors, including the health of the power grid.
Some power grids therefore impose a ramp rate on small power sources that limits the rate of change at which power is permitted to be provided to the power grid. For example, the Puerto Rico Electrical Power Authority imposes a limit of 10% of installed capacity for one-minute ramps on both PV and wind-based power generation. It thus would be desirable to provide a system that enables local electrical networks with small power sources to avoid exceeding applicable ramp rates in a cost-efficient fashion.